Re: PATCH: 0/6 [2nd try]: Add AVX support

Mark Kettenis
2010-03-07T19:49:21Z

> Date: Sun, 7 Mar 2010 11:09:59 -0800
> From: Nathan Froyd <froydnj@codesourcery.com>
>
> On Sun, Mar 07, 2010 at 08:40:10AM -0800, H.J. Lu wrote:
> > My first approach works here since XMM and YMM register have the same
> > register numbers. We can solve it with 2 alternatives:
> >
> > 1. Give a different DWARF register number for YMM register,
> > which is an incompatible ABI change.
> > 2. Implement YMM registers as a super set of XMM registers, which
> > is my first approach.
>
> The third alternative--again, what's adopted for the PPC SPE 64-bit
> registers--is to give %ymmNh their own DWARF register numbers. I
> suppose it's also ABI-incompatible, but it seems like it fits with your
> approach much better than either of the above alternatives.

I don't think that would be a good idea. It means you can't refer to
something stored in a %ymmN register with a single register number.
The compiler will have to use a more complicated expression (which may
not be possible for older debug info formats) for these. As a result,
things like "info address" become rather useless.